A coating film containing phosphorus atoms and metal atoms such as aluminum as constituents is conventionally known. For example, a formed product of an organic polymer coated with a gas permeation preventing film composed of metal orthophosphate mainly containing aluminum is known (Patent Literature 1: JP 55 (1980)-46969 A). JP 55-46969 A discloses a method for forming a gas permeation preventing film by applying a dispersion or solution of metal orthophosphate to a formed product of an organic polymer. JP 55-46969 A discloses, as a method for forming the dispersion or solution of metal orthophosphate, a method of separately dissolving an aluminum ion source and a phosphorus ion source each in a medium, followed by mixing these solutions.
Also known is a gas barrier layered film in which an inorganic oxide-deposited layer is provided on a base film composed of a plastic film, and a coating layer of metal phosphate is provided on this inorganic oxide-deposited layer (Patent Literature 2: JP 2006-116737 A). JP 2006-116737 A discloses, as a method for forming a coating layer of metal phosphate, a method of applying a specific coating liquid obtained by mixing a phosphate ion-containing solution and a metal ion-containing solution.
Meanwhile, a method of using aluminophosphate for reducing the surface roughness of a base such as iron and glass is known (Patent Literature 3: JP 2006-515535 T). JP 2006-515535 T discloses a method of forming an amorphous aluminophosphate compound on a base such as iron and glass by applying a precursor of the aluminophosphate compound containing aluminum ions and phosphoric acid ester in a liquid medium on the base. JP 2006-515535 T discloses that an absorption peak due to vibration of Al—O—P group appears in the range of 1180 to 1280 cm−1 (specifically, at 1207 cm−1) in the infrared absorption spectrum of a coating layer which has been formed on stainless steel and subjected to heat treatment at 500° C. for 5 minutes.
Further, a composite composed of a base such as metal, metal alloy and plastic, and a coating component containing a specific aluminum phosphate compound is also known (Patent Literature 4: JP 2008-516015 T). JP 2008-516015 T discloses a method of forming a coating using a solution containing aluminum salt and phosphoric acid ester in an organic solvent. JP 2008-516015 T discloses that the coating component includes a structural site that absorbs the radiation at about 1230 cm−1 in the infrared absorption spectrum.